1. Field of the Invention
The present invention relates to a power supply voltage monitoring circuit capable of decreasing a minimum operating power supply voltage in an electronic circuit so that the electronic circuit may operate with low voltage, and to an electronic circuit including the power supply voltage monitoring circuit.
2. Description of the Related Art
A related-art power supply voltage monitoring circuit is now described. FIG. 5 is a circuit diagram illustrating the related-art power supply voltage monitoring circuit. The related-art power supply voltage monitoring circuit includes a current source circuit 110, an impedance circuit 120, a bias voltage source 401, a comparator 402, a ground terminal 100, a power supply terminal 101, and an output terminal 102. The current source circuit 110 and the impedance circuit 120 form a signal output circuit 140. The bias voltage source 401 and the comparator 402 form a signal voltage monitoring circuit 130.
After a power supply voltage VDD is input to the power supply terminal 101, the signal output circuit 140 outputs a signal representing saturation characteristics with respect to the power supply voltage VDD, and the signal voltage monitoring circuit 130 compares the signal output from the signal output circuit 140 and the power supply voltage VDD to each other and outputs a signal representing that the signal output from the signal output circuit 140 is normal.
This configuration may decrease a minimum operating power supply voltage in an electronic circuit, thereby being capable of efficiently using the power supply voltage (see, for example, FIG. 1 of Japanese Patent Application Laid-open No. 2010-166184).
In the related-art power supply voltage monitoring circuit, however, the signal voltage monitoring circuit is formed by a comparator, and hence there is a problem in that the signal voltage monitoring circuit has a large circuit scale. Further, there is another problem in that the signal voltage monitoring circuit has high power consumption and it is difficult to decrease power consumption of the power supply voltage monitoring circuit.